An encoder unit of the initially mentioned type is known from EP 1 055 915 (PWB-Ruhlatec GmbH) wherein the encoder consists of an interlocking housing which, at the end face, is flanged on to a motor which, at least in one flange plane, comprises a motor shaft projecting into the housing. The housing consists of a base plate with an inner housing part and an upper housing part, which two parts, for assembly purposes, can be interlocked relative to one another, wherein bayonet segments are arranged on the inner housing part, which bayonet segments engage matching recesses in the upper housing part. During a rotational movement for form-fittingly and positively connecting the bayonet segments, wedge-shaped guiding faces slide on one another, so that the upper housing part is separated from the base plate, as a result of which the timing disc is “cleared” on the motor shaft.
The German utility model DE 291 20 932 U1 (PWB-Ruhlatec Industrieprodukte GmbH) proposes a motor/sensor system wherein on a printed circuit board there are provided at least two contact pins for supplying power to the electric motor fixed by a fixing bracket on the printed circuit board. During the fixing process, the timing disc secured on the motor shaft is positioned in the slot of a sensor/emitter unit. Through a semi-circular cut-out in the fixing bracket, the shaft end of the sensor/emitter unit is self-centringly positioned with reference to the timing disc secured on the shaft end of the electric motor. However, said fixing is open on all sides, so that the prior art motor/sensor system is exposed to environmental influences.
Encoder systems are subject to stringent requirements in respect of reliability under fluctuating temperatures, in respect of accurate positioning and resolution quality. As such encoder systems are mass-produced, there is a need for designs which are easy to produce and which consist of a few simple components which are not subject to failure.
For some time now, the high surface quality of the motor shaft is used for fixing the timing discs via a timing disc hub by means of a press fit. As it is necessary to observe very close tolerances, the pressure forces are correspondingly high. After the assembly process has been completed, the timing disc has to be “cleared” so to speak, which in EP 1 055 915 is achieved by rotating wedge-shaped bayonet faces. However, the prior art system is not suitable for larger timing disc diameters and larger printed circuit boards.
It is therefore the object of the present invention to provide an encoder unit and a process of assembling same which can be carried out quickly and easily and with a minimum of tools. The pre-assembled unit is to be protected against dirt and mechanical damage to the timing disc. A further requirement consists in that the encoder can be tested as a component. After the unit has been pre-assembled on the electric motor or on some other driven shaft, there shall be no need for individual parts of the unit to be removed or newly added.